1. Field of the Invention
This invention relates to force transducers (actuators) and more specifically to a force transducer suitable for use e.g. in a lithography machine.
2. Background
In the mechanical engineering field, it is a well known problem to provide precision motion with minimum vibration. For instance such motion is frequently needed in the context of machine tools and lithography, e.g. stepper and scanner machines used in the semiconductor industry. Typically the goal is to provide precision location of, for instance, an x-y stage in three dimensions. (Typically the two horizontal directions are denoted x and y and the vertical direction is designated z.) Such stages are used for instance to position a workpiece such as a wafer or a reticle. An example of a x-y stage is disclosed in U.S. patent application Ser. No. 09/287,545 filed Apr. 6, 1999, commonly invented, entitled "X-Y Stage With Movable Magnet Plate" now U.S. Pat. No. 6,130,490, issued Oct. 10, 2000, incorporated herein by reference. That discloses an x-y stage suitable for supporting a reticle in a lithography system.
The particular x-y stage is supported underneath by ball and flat spherical bearing system with a set of e.g. four relatively large diameter hard spheres supporting the weight of the stage on an underlying support plate. The stage moves in two dimensions (x and y) on the support plate. The spheres are not continuously constrained in a cage in one embodiment, unlike a conventional ball bearing, but instead move relatively freely to the stage on the underlying support plate surface. There are associated bearing support surfaces on the underside of the stage and on the top surface of the underlying support plate for the balls to move upon. These surfaces are specially hardened regions.
In that system, as is typical, some vertical motion (z direction) is used to keep the stage at a particular vertical location, for instance for focusing purposes. This vertical positioning may occur continuously while the system is in operation.
Therefore there is presented the problem of providing an accurate and precise z axis positioning in such a system. In certain such systems it is desirable to avoid transmission of vibration through the z direction positioning since the stage must be kept free of vibration.